Stabilized water-soluble polymer powders on the basis of polyoxy alkylene glycol carboxylates and method for producing same

Abstract

Stabilized, water-soluble polymer powders based on polyoxyalkylene glycol carboxylates are described, wherein the powders comprise from 0.01 to 10% by weight of a stabilizer selected from the group consisting of phenols, amines, phosphites, thioethers, and also thioacids, and where the stabilizer was added in liquid or dissolved form to the aqueous polymer solution prior to its conversion into the powder form. The polymer powders thus protected against autoignition and oxidative degradation have unexpectedly high thermooxidative stability, even on exposure to high temperatures and oxidizing action (air, oxygen).

What is claimed is:  
     
       1. A stabilized, water-soluble polymer powder based on polyoxyalkylene glycol carboxylates, wherein the powder comprises a stabilizer selected from the group consisting of phenols, amines, phosphites, thioethers, and thioacids, in an amount adequate for stabilization, and said powder is obtained by adding the stabilizer in liquid or dissolved form to the aqueous polymer solution prior to its conversion into the powder form. 
     
     
       2. The polymer powder as claimed in  claim 1 , wherein the polymers have been built up from monomers based on unsaturated carboxylic acids or derivatives of these and from oxyalkylene glycol alkenyl ethers. 
     
     
       3. The polymer powder as claimed in  claim 1 , wherein 
       the polymers contain an unsaturated carboxylic acid as main chain and polyalkylene oxide side chains bonded via ester groups.  
     
     
       4. The polymer powder as claimed in  claim 1 , wherein the polymers contain other vinyl- and/or acrylate-based monomers. 
     
     
       5. The polymer powder as claimed in  claim 1 , wherein the amount of the stabilizer is from 0.01 to 10% by weight and in particular from 0.1 to 1% by weight, based on the polymer powder. 
     
     
       6. The polymer powder as claimed in  claim 1 , wherein the stabilizer comprises an alkylated monophenol having at least one alkyl radical or an alkylated monophenol having from 1 to 18 carbon atoms. 
     
     
       7. The polymer powder as claimed in  claim 1 , wherein the stabilizer comprises an alkylated hydroquinone comprising at least one alkyl radical having from 1 to 18 carbon atoms. 
     
     
       8. The polymer powder as claimed in  claim 5 , wherein the stabilizer comprises at least one phenol compound selected from the group consisting of an alkylidenebisphenol having a C 1 -C 4 -alkylidene radical and an alkylidenebisphenol having a sterically hindered polynuclear phenol. 
     
     
       9. The polymer powder as claimed in  claim 1 , wherein the stabilizer comprises a phenolic benzyl compound. 
     
     
       10. The polymer powder as claimed in  claim 1 , wherein the stabilizer comprises at lest one of a phenol thioether compound or a biphenyl thioether compound. 
     
     
       11. The polymer powder as claimed in  claim 1 , wherein the stabilizer is an acylaminophenol. 
     
     
       12. The polymer powder as claimed in  claim 1 , wherein the stabilizer is an ester of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid or β-(5-tert-butyl-4-hydroxy-3-methylphenyl) propionic acid. 
     
     
       13. The polymer powder as claimed in  claim 1 , wherein the stabilizer is an amide of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid. 
     
     
       14. The polymer powder as claimed in  claim 1 , wherein the stabilizer is selected form the group consisting of a secondary amine a tertiary amine, and an N-heterocycle. 
     
     
       15. The polymer powder as claimed in  claim 14 , wherein the N-heterocycle is at least one N-heterocycle selected from the group consisting of a substituted phenothiazine, an unsubstituted phenothiazine, a substituted benzothiazine, an unsubstituted benzothiazine, a substituted quinoline, and an unsubstituted quinoline. 
     
     
       16. The polymer powder as claimed in  claim 1 , wherein the stabilizer is a phosphite having at least one radical selected from the group consisting of an aliphatic radical, an araliphatic radical and an aromatic radical. 
     
     
       17. The polymer powder as claimed in  claim 1 , wherein the stabilizer based on a thioether comprises an ester of thiodiacetic acid and/or thiodipropionic acid. 
     
     
       18. The polymer powder as claimed in  claim 1 , wherein the stabilizer. Is at least one thioacid selected from the group consisting of dithiocarbamic acid, dithiophosphoric acid, a salt of dithiocarbamic acid, and a salt of dithiophosphoric acid. 
     
     
       19. The polymer powder as claimed in  claim 1 , wherein the particle size of the powder is from 10 to 100 μm. 
     
     
       20. The polymer powder as claimed in  claim 1 , wherein the powder also comprises up to 5% by weight of a water-soluble aminosulfonic acid compound. 
     
     
       21. The polymer powder as claimed in  claim 20 , wherein the aminosulfonic acid compound is selected from the group consisting of amidosulfonic acid, taurine free acid, taurine salt, and a combination thereof. 
     
     
       22. The polymer powder as claimed in  claim 1 , wherein when a specimen of the powder is heated at 140° C. for 24 h the temperature in the interior of the specimen does not exceed 200° C. 
     
     
       23. A process for preparing a stabilized, water-soluble polymer powder based on polyoxyalkylene glycol carboxylates comprising the steps of: 
       (a) adding a stabilizer selected from the group consisting of phenols, amines, phosphites, thioethers, and thioacids, in an amount adequate for stabilization, in liquid or dissolved form, to an aqueous solution of a polymer based on polyoxyalkylene glycol carboxylates, to form a microemulsion, and then  
       (b) converting the polymer into the powder form by removing the liquid phase.  
     
     
       24. The process as claimed in  claim 23 , wherein the aqueous polymer solution has a solids content of from 10 to 50% by weight. 
     
     
       25. The process as claimed in  claim 23 , wherein the pH of the aqueous polymer solution is adjusted to 6-10 prior to conversion into the powder form. 
     
     
       26. The process as claimed in  claim 25 , wherein the pH of the aqueous polymer solution is adjusted to 7-9 prior to conversion into the powder form. 
     
     
       27. The process as claimed in  claim 14 , wherein said secondary amine and said tertiary amine have aliphatic, araliphatic, aromatic or cyclic radicals. 
     
     
       28. The process as claimed in  claim 23 , wherein the liquid phase is removed by drying. 
     
     
       29. The process as  claim 28 , wherein said drying is spray drying.